CN115385400B - High-nickel low-cobalt cathode material, preparation method thereof and lithium ion battery - Google Patents
High-nickel low-cobalt cathode material, preparation method thereof and lithium ion battery Download PDFInfo
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- CN115385400B CN115385400B CN202211322604.9A CN202211322604A CN115385400B CN 115385400 B CN115385400 B CN 115385400B CN 202211322604 A CN202211322604 A CN 202211322604A CN 115385400 B CN115385400 B CN 115385400B
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Abstract
The invention discloses a high-nickel low-cobalt cathode material, a preparation method thereof and a lithium ion battery, and relates to the technical field of lithium batteries. Waste gas generated in the processes of primary sintering and secondary sintering in the preparation process of the cathode material is utilized, the waste gas generated in the primary sintering is used in the washing process and the coating process after mixing, and the waste gas generated in the secondary sintering and/or the waste gas generated in the primary sintering cooling section are introduced in the drying process after washing. The preparation method can reduce the dissolution speed of LiOH on the surface in the water washing process and delay the generation of NiO rock salt phase on the surface of the material. In addition, a similar lithium supplement agent is added in the coating process to react with the coating, which is beneficial to synthesizing the coating with better ionic conductivity in the secondary sintering process and improving the cycle performance of the material.
Description
Technical Field
The invention relates to the technical field of lithium batteries, in particular to a high-nickel low-cobalt positive electrode material, a preparation method thereof and a lithium ion battery.
Background
High nickel positive electrode materials, such as nickel-cobalt-manganese positive electrode materials, have good cycle performance, higher specific capacity, good safety and low cost, and thus are widely researched and applied. The preparation of the nickel-cobalt-manganese anode material generally comprises the steps of preparing a nickel-cobalt-manganese precursor by a coprecipitation method, and then sintering to obtain the anode material.
The nickel-cobalt-manganese cathode material is sintered in the first sintering and the second sintering by using oxygen as sintering atmosphere, a large amount of waste gas is discharged into the atmosphere after sintering, and the waste gas contains a certain amount of lithium compounds, so that the air pollution is easily caused, and the waste of energy is also caused.
In view of this, the invention is particularly proposed.
Disclosure of Invention
The invention aims to provide a high-nickel low-cobalt cathode material, a preparation method thereof and a lithium ion battery, and aims to use waste gas in the preparation process of the cathode material so as to remarkably improve the electrochemical performance of the cathode material.
The invention is realized in the following way:
in a first aspect, the present invention provides a method for preparing a high-nickel low-cobalt cathode material, comprising:
respectively sintering the prepared single crystal nickel-cobalt-manganese precursor and polycrystalline nickel-cobalt-manganese precursor with a lithium source in an oxygen atmosphere to obtain a nickel-cobalt-manganese single crystal material and a nickel-cobalt-manganese polycrystalline material, mixing the nickel-cobalt-manganese single crystal material and the nickel-cobalt-manganese polycrystalline material, then sequentially washing, carrying out solid-liquid separation and drying, mixing the dried material with a coating agent, and then carrying out secondary sintering;
wherein the particle size of the single crystal nickel-cobalt-manganese precursor is smaller than that of the polycrystalline nickel-cobalt-manganese precursor;
the preparation process of the water washing solution adopted in the water washing process comprises the following steps: mixing waste gas generated by primary sintering with water;
the atmosphere adopted in the drying process is selected from at least one of waste gas generated in the secondary sintering and waste gas generated in the primary sintering cooling section;
and introducing waste gas generated by primary sintering in the process of mixing the dried material and the coating agent.
In an alternative embodiment, the primary sintering process comprises:
mixing the single crystal nickel-cobalt-manganese precursor with a lithium source, and sintering for 10-15 h at 810-925 ℃ in an oxygen atmosphere to obtain a nickel-cobalt-manganese single crystal material;
mixing a polycrystalline nickel cobalt manganese precursor with a lithium source, and sintering for 8-12 h under the conditions of an oxygen atmosphere and 700-850 ℃ to obtain a nickel cobalt manganese polycrystalline material;
wherein the lithium source is at least one selected from lithium hydroxide, lithium nitrate and lithium chloride;
the D50 of the single crystal nickel-cobalt-manganese precursor particles is 3-4 mu m, and the D50 of the polycrystalline nickel-cobalt-manganese precursor particles is 8-10 mu m.
In an alternative embodiment, the single crystal nickel cobalt manganese precursor and the polycrystalline nickel cobalt manganese precursor have the chemical formula Ni x Co y Mn z (OH) 2 ，x+y+z＝1；x=0.65~0.95；y= (1-x)/(x+1)；
When the single crystal nickel cobalt manganese precursor and the polycrystalline nickel cobalt manganese precursor are sintered for one time, controlling the molar ratio of lithium elements in the precursor and a lithium source to be 1: m, m =1.04-1.07.
In an optional embodiment, the single crystal nickel-cobalt-manganese precursor and the polycrystalline nickel-cobalt-manganese precursor are prepared by a coprecipitation reaction, and the preparation process includes:
mixing nickel salt, cobalt salt and manganese salt according to the molar ratio of nickel, cobalt and manganese of x, y and z, and carrying out coprecipitation under the condition of adding a precipitator and a chelating agent, wherein the coprecipitation process is controlled to be carried out under an inert atmosphere, the pH value of a system is controlled to be 10.5-11.5, the temperature is controlled to be 45-55 ℃, and when a precursor with a required size is obtained through deposition, washing and drying are carried out;
wherein the precipitator is a sodium hydroxide solution with the concentration of 3-5 mol/L, and the chelating agent is an ammonia water solution with the concentration of 8-12 mol/L.
In an alternative embodiment, the process of blending the nickel cobalt manganese single crystal material and the nickel cobalt manganese polycrystalline material comprises: crushing the nickel-cobalt-manganese single crystal material to a D50 value of 3-5 mu m, crushing the nickel-cobalt-manganese polycrystalline material to a D50 value of 9-11 mu m, and mixing the crushed nickel-cobalt-manganese single crystal material and the crushed nickel-cobalt-manganese polycrystalline material according to a mass ratio of 2.
In an alternative embodiment, the preparation of the aqueous wash solution comprises: introducing waste gas generated by primary sintering into water, wherein the volume of the waste gas per liter of water is 3m 3 -5m 3 ；
During water washing, the mixed material is placed in a water washing solution and is washed with water under the stirring condition; controlling the mass of the material which is correspondingly blended per liter of washing solution to be 0.5kg-2kg;
when washing with water, the stirring frequency is controlled to be 100Hz-200Hz, and the stirring time is 10min-20min.
In an optional embodiment, after washing, performing solid-liquid separation, drying the obtained solid material under the condition of stirring, and introducing waste gas at the speed of 40L/min-60L/min in the drying process; controlling the stirring speed to be 50-200 rpm, and the drying time to be 4-8 h;
wherein, the solid-liquid separation is carried out by adopting a filter pressing mode.
In an optional embodiment, the dried material and the coating agent are mixed under the condition of waste gas generated in a primary sintering temperature rising region, and secondary sintering is carried out after mixing;
in the mixing process, the stirring speed is controlled to be 400rpm-800rpm, and the stirring time is controlled to be 20min-60min; controlling the sintering temperature of the secondary sintering to be 280-550 ℃ and the sintering time to be 4-8 h;
the coating agent is selected from at least one of boric acid, aluminum hydroxide and titanium oxide; the coating amount of the coating element is controlled to be 500ppm-1500ppm.
In a second aspect, the present invention provides a high nickel and low cobalt cathode material prepared by the preparation method according to any one of the foregoing embodiments.
In a third aspect, the present invention provides a lithium ion battery, including the high nickel and low cobalt cathode material of the foregoing embodiments.
The invention has the following beneficial effects: waste gas generated in the processes of primary sintering and secondary sintering in the preparation process of the cathode material is utilized, the waste gas generated in the primary sintering is used in the washing process and the coating process after mixing, and the waste gas generated in the secondary sintering and/or the waste gas generated in the primary sintering cooling section are introduced in the drying process after washing, so that the cycle performance of the cathode material can be remarkably improved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and those skilled in the art can also obtain other related drawings based on the drawings without inventive efforts.
FIG. 1 is a flow chart for the preparation of single crystals and polycrystals;
fig. 2 is an XRD pattern of the product prepared in example and comparative example.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
In order to effectively and reasonably utilize the waste gas generated in the preparation process of the high nickel material, the embodiment of the invention provides a preparation method of a high nickel and low cobalt cathode material, please refer to fig. 1, which comprises the following steps:
s1, preparation of nickel-cobalt-manganese precursor
The preparation method of the nickel-cobalt-manganese precursor is not limited, and the nickel-cobalt-manganese precursor can be prepared by a common coprecipitation method, and a monocrystalline nickel-cobalt-manganese precursor and a polycrystalline nickel-cobalt-manganese precursor are respectively prepared, wherein the grain size of the polycrystalline nickel-cobalt-manganese precursor is larger, and the grain size of the monocrystalline nickel-cobalt-manganese precursor is smaller, and the polycrystalline nickel-cobalt-manganese precursor is used for doping subsequent large and small grains. Generally speaking, the large-particle product has higher capacity, the small-particle product has more excellent cycle performance, and the large-particle and small-particle doping can be utilized to prepare the product with better comprehensive performance and compact structure.
In some embodiments, the single crystal nickel cobalt manganese precursor particles D50 are between 3 μm and 4 μm (e.g., 3.0 μm, 3.5 μm, 4.0 μm, etc.) and the polycrystalline nickel cobalt manganese precursor particles D50 are between 8 μm and 10 μm (e.g., 8 μm, 9 μm, 10 μm, etc.).
In some embodiments, the single crystal nickel cobalt manganese precursor and the polycrystalline nickel cobalt manganese precursor have the formula Ni x Co y Mn z (OH) 2 X + y + z =1; x =0.65 to 0.95; y = (1-x)/(x + 1). For example, x may be 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, etc., and y is rounded to leave two significant digits.
In some embodiments, the single crystal nickel cobalt manganese precursor and the polycrystalline nickel cobalt manganese precursor are prepared by a coprecipitation reaction, and the preparation process includes: mixing nickel salt, cobalt salt and manganese salt according to the molar ratio of nickel, cobalt and manganese of x, y and z, initiating coprecipitation under the condition of adding a precipitator and a chelating agent, controlling the coprecipitation process under an inert atmosphere, controlling the pH value of a system to be 10.5-11.5 (such as 10.5, 11.0, 11.5 and the like) and the temperature to be 45-55 ℃ (45 ℃, 50 ℃, 55 ℃ and the like), and performing water washing and drying after a precursor with a required size is obtained by deposition. Residual chemical substances can be effectively removed by multiple water washes, and the drying can be carried out in an oven at 100-150 ℃ (such as 120 ℃) for about 20-30 h (such as 24 h).
It should be noted that the coprecipitation method is a common method for preparing a nickel-cobalt-manganese precursor, and is obtained by coprecipitation of nickel salt, cobalt salt and manganese salt under an alkaline condition.
In some embodiments, the precipitant may be, but is not limited to, a sodium hydroxide solution of 3mol/L to 5mol/L, and the specific concentration may be 3mol/L, 4mol/L, 5mol/L, or the like; the chelating agent can be but not limited to an ammonia solution with the concentration of 8mol/L-12mol/L, and the specific concentration can be 8mol/L, 10mol/L, 12mol/L and the like.
Specifically, the inert gas may be, but is not limited to, nitrogen, and the nickel, cobalt and manganese salts may be, but is not limited to, sulfates.
S2, primary sintering
And respectively sintering the prepared single crystal nickel-cobalt-manganese precursor and the polycrystalline nickel-cobalt-manganese precursor with a lithium source in an oxygen atmosphere to obtain the nickel-cobalt-manganese single crystal material and the nickel-cobalt-manganese polycrystalline material. Respectively sintering the single-crystal nickel-cobalt-manganese precursor and the polycrystalline nickel-cobalt-manganese precursor for one time to respectively obtain a nickel-cobalt-manganese single-crystal material and a nickel-cobalt-manganese polycrystalline material, wherein the sintering atmosphere can be an oxygen atmosphere of more than 50%.
In practical operation, the process of primary sintering comprises the following steps: mixing the single-crystal nickel-cobalt-manganese precursor with a lithium source, and sintering the mixture for 10 to 15 hours (such as 10 hours, 12 hours, 15 hours and the like) in an oxygen atmosphere at the temperature of between 810 and 925 ℃ (such as 810, 850, 900, 925 ℃ and the like) to obtain the micron-grade nickel-cobalt-manganese single-crystal material. Similarly, the polycrystalline nickel cobalt manganese precursor is mixed with a lithium source and sintered for 8h to 12h (such as 8h, 10h, 12h and the like) under the conditions of 700 ℃ to 850 ℃ (such as 700 ℃, 750 ℃, 800 ℃, 850 ℃ and the like) in an oxygen atmosphere to obtain the nickel cobalt manganese polycrystalline material. Sintering at a higher temperature to obtain a nickel-cobalt-manganese single crystal material, and sintering at a lower temperature to obtain a nickel-cobalt-manganese polycrystalline material for a subsequent blending process.
In some embodiments, the mixing of the precursor and the lithium source may be performed in a ball mill pot to improve the uniformity of the mixing of the raw materials.
In some embodiments, the precursor (Ni) is controlled during a single sintering of the single crystal nickel cobalt manganese precursor and the polycrystalline nickel cobalt manganese precursor x Co y Mn z (OH) 2 ) And a lithium source (e.g., liOH. H) 2 The molar ratio of lithium element in O) is 1: m, m =1.04-1.07, such as 1.04, 1.05, 1.06, 1.07, etc.
In some embodiments, the lithium source is selected from at least one of lithium hydroxide, lithium nitrate, and lithium chloride, and the lithium source may be any one or more of the above.
S3, blending
The nickel-cobalt-manganese single crystal material and the nickel-cobalt-manganese polycrystalline material are mixed, so that the preparation of the product with excellent capacity and cycle performance is facilitated.
In some embodiments, the process of blending the nickel cobalt manganese single crystal material and the nickel cobalt manganese polycrystalline material comprises: pulverizing the nickel-cobalt-manganese single crystal material to a D50 of 3 μm to 5 μm (e.g., 3 μm, 4 μm, 5 μm, etc.), pulverizing the nickel-cobalt-manganese polycrystalline material to a D50 of 9 μm to 11 μm (e.g., 9 μm, 10 μm, 11 μm, etc.), and mixing the pulverized nickel-cobalt-manganese single crystal material and the nickel-cobalt-manganese polycrystalline material in a mass ratio of 2.
Specifically, the crushing process of the nickel-cobalt-manganese single crystal material can use a jaw crusher, a double-roll mill, a jet mill and the like, and is not limited herein. The crushing process of the nickel-cobalt-manganese polycrystalline material can adopt a jaw crusher, a roll crusher, a mechanical mill and the like, and is not limited herein.
S4, intermediate treatment
And (4) sequentially carrying out water washing, solid-liquid separation and drying on the blending product obtained in the step (S3), removing residual alkali through water washing, obtaining a solid material through solid-liquid separation, and drying the solid material to remove moisture.
Specifically, the preparation process of the water washing solution adopted in the water washing process comprises the following steps: mixing waste gas (oxygen containing lithium compound) generated in the primary sintering with water; the atmosphere used in the drying process is at least one of the waste gas generated in the secondary sintering and the waste gas generated in the primary sintering cooling section, the atmosphere used in the drying process is the waste gas with the temperature of more than 120 ℃, the component is pure oxygen, and the lithium compound is hardly contained.
The waste gas (oxygen containing lithium compounds) generated by the primary sintering of high nickel is introduced into the aqueous solution to synthesize a solution with a certain Li content, which is used as a water washing solution, so that the dissolution speed of residual alkali is reduced, and the generation of a NiO rock salt phase on the surface of the material is delayed. The waste gas (higher than 120 ℃, pure oxygen and hardly containing lithium compounds) generated in the secondary sintering or primary sintering cooling section of high nickel is directly introduced into a container capable of stirring, the material is dried by using the waste heat of the waste gas while stirring, and the drying in the oxygen atmosphere can prevent the residual alkali on the surface of the material from reacting with water and carbon dioxide in the air.
In some embodiments, the preparation of the aqueous wash solution comprises: introducing waste gas generated by primary sintering into water to synthesize certain Li + Solution of content, volume of exhaust gas per liter of water is 3m 3 -5m 3 E.g. 3m 3 、4m 3 、5m 3 And the volume of the gas is measured at normal temperature and pressure. During water washing, the mixed material is placed in a water washing solution and is washed with water under the stirring condition; the weight of the material blended is controlled to be 0.5kg-2kg, such as 0.5kg, 1.0kg, 1.5kg, 2.0kg, etc. per liter of the washing solution.
In some embodiments, during the water washing, the stirring frequency is controlled to be 100Hz-200Hz, the stirring time is controlled to be 10min-20min, and the residual alkali is sufficiently removed by stirring and controlling the water washing time. The stirring frequency of the stirrer can be 100Hz, 150Hz, 200Hz and the like, and the stirring time can be 10min, 15min, 20min and the like.
In some embodiments, the water washing is followed by solid-liquid separation, which may be, but is not limited to, a pressure filtration method, which is used to remove liquid materials more fully.
In some embodiments, the obtained solid material is dried under stirring, and waste gas is introduced at a speed of 40L/min-60L/min during the drying process; controlling the stirring speed to be 50rpm-200rpm for 6h (the operation can be carried out in a mode of stirring for 10min and stopping for 10 min), and controlling the drying time to be 4h-8h; the material is dried by using the waste heat of the waste gas while stirring, and the drying in the oxygen atmosphere can prevent the residual alkali on the surface of the material from reacting with water and carbon dioxide in the air. Specifically, the drying may be performed in a VC mixer, the stirring rate may be controlled to be 50rpm, 100rpm, 150rpm, 200rpm, etc., the stirring time may be 4 hours, 6 hours, 8 hours, etc., and the rate of waste gas introduction may be 40L/min, 50L/min, 60L/min, etc.
S5, secondary sintering
Mixing the dried material with a coating agent and then carrying out secondary sintering; and introducing waste gas generated by primary sintering in the process of mixing the dried material and the coating agent.
It should be noted that the waste gas (containing oxygen of lithium compound) generated by the material passing through the primary sintering temperature rising zone after drying, and the metal oxide added in the material as a coating agent, is helpful for synthesizing a coating material with better ionic conductivity in the secondary sintering process, and improves the cycle performance of the material.
In some embodiments, the dried material and the coating agent are mixed under the condition of waste gas generated in the primary sintering temperature rising region, and secondary sintering is performed after mixing. The lithium content of waste gas generated in the primary sintering temperature rising area is higher, and the method is more suitable for being used in a coating stage. In the mixing process, the stirring speed is controlled to be 400rpm-800rpm, such as 400rpm, 600rpm, 800rpm and the like; stirring for 20min-60min, such as 20min, 40min, 60min, etc.
In some embodiments, the atmosphere for the secondary sintering may be air or oxygen, preferably oxygen. Controlling the sintering temperature of the secondary sintering to be 280-550 ℃, such as 280 ℃, 300 ℃, 350 ℃, 400 ℃, 450 ℃, 500 ℃, 550 ℃ and the like; the sintering time is 4h-8h, such as 4h, 6h, 8h and the like.
In some embodiments, the coating agent is selected from at least one of boric acid, aluminum hydroxide, titanium oxide, that is, the coating element may be B, al, ti, or the like. The coating amount of the coating element is controlled to be 500ppm-1500ppm, such as 500ppm, 1000ppm, 1500ppm, etc.
It is added that the sintering process is generally carried out in a tubular furnace, the furnace body is divided into a temperature rising section, a heat preservation section and a temperature reduction section, the working time of each section is different, and waste gas generated by each section can be collected respectively.
The embodiment of the invention also provides a high-nickel low-cobalt cathode material which is prepared by the preparation method, has higher capacity and better cycle performance, can be further prepared into a lithium ion battery, and has very good market application prospect.
Specifically, the chemical formula of the high-nickel low-cobalt cathode material is Li m Ni x Co y Mn z ，1.04≤m≤1.07，x+y+z＝1；x=0.65~0.95；y= (1-x)/(x+1)。
The features and properties of the present invention are described in further detail below with reference to examples.
Example 1
The embodiment provides a preparation method of a high-nickel low-cobalt cathode material, which comprises the following steps:
(1) Preparation of nickel-cobalt-manganese precursor
NiSO was injected into a continuously stirred 50L reactor 4 ·6H 2 O、CoSO 4 ·7H 2 O and MnSO 4 ·5H 2 And (3) dissolving O in water to form a solution, controlling the total molar concentration of nickel, cobalt and manganese to be 2mol/L and the molar ratio of Ni, co and Mn to be = x, y and z, and introducing nitrogen all the time in the process, wherein the temperature is kept constant at 50 ℃. While stirring the reactor, 4mol/L NaOH solution (precipitant) and 10mol/L NH were added 3 ·H 2 O solution (chelating agent) to keep the pH value of the system at 11.0 and the ammonia value at 10g/L. After the precipitation was completed, it was washed with distilled water and then dried in an oven at 120 ℃ for 24 hours.
The single crystal precursor particles D50 prepared by the method are 3-4 μm, and the polycrystalline precursor particles D50 are 8-10 μm.
(2) Primary sintering
The single crystal precursor particles Ni prepared in the step (1) are put into x Co y Mn z (OH) 2 Particles and LiOH 2 Mixing O in ball mill pot, ni x Co y Mn z (OH) 2 :LiOH•H 2 O =1, the mixture was calcined at M2 ℃ for 12h in an oxygen atmosphere to give a micron-sized single crystal LiNixCoyMnzO 2 And (3) granules.
Subjecting the polycrystalline precursor prepared in step (1)Bulk grain Ni x Co y Mn z (OH) 2 Particles and LiOH 2 Mixing O in ball mill pot, ni x Co y Mn z (OH) 2 :LiOH•H 2 O = 1M, and the mixture was calcined at M1 ℃ for 10h in an oxygen atmosphere to obtain polycrystalline LiNi x Co y Mn z O 2 And (3) particles.
(3) Blending of
The single crystal LiNixCoyMnzO obtained in the step (2) 2 Crushing the particles to D50=4.0 + -1.0 μm, polycrystalline LiNi x Co y Mn z O 2 The particles were crushed to D50=10.0 ± 1.0 μm. And blending the crushed materials according to the mass ratio of single crystal to polycrystal of 2.
(4) Intermediate treatment
Will yield 20m of one sintering 3 The waste gas is introduced into 5L pure water to synthesize certain Li + And (4) taking the solution with the content as a water washing solution, adding 5kg of the material mixed in the step (3) after the water washing solution is finished, stirring for 15min by using a stirrer according to the frequency of 150Hz, then putting the material into a filter press for filter pressing for 30min, putting the material after the filter pressing into a VC mixer, stirring for 6h at the speed of 100rpm (stopping stirring for 10 min), introducing waste gas (more than 120 ℃) generated in a primary sintering cooling section at the speed of 50L/min all the time, and drying the material after 6 h.
(5) Secondary sintering
And adding a coating agent (boric acid) into the dried material, controlling the coating amount of B to be 1000ppm, simultaneously switching the introduced gas to the waste gas generated in the primary sintering heating area (the introduction rate is 10L/min), stirring at 600rpm for 30min, and taking out. And sintering the mixed material at the temperature of M3 for 6 hours, and sieving the mixed material by a 400-mesh sieve to obtain a target product.
The differences between the embodiments 1 to 7 are only in the parameter values, which are as follows:
example 1: lithium complex m =1.06, x =0.82, y =0.10, z =0.08; the temperature M1=770 ℃, M2=850 ℃, M3=300 ℃, and the exhaust gas is respectively introduced in the processes of coating B1000 ppm, washing, drying and coating.
Example 2: lithium complex m =1.04, x =0.65, y =0.25, z =0.15; the temperature M1=850 ℃, M2=925 ℃, M3=295 ℃, the coating B is 1000ppm, and waste gas is respectively introduced in the processes of water washing, drying and coating.
Example 3: lithium complex m =1.05, x =0.75, y =0.14, z =0.11; the temperature M1=810 ℃, the temperature M2=880 ℃, the temperature M3=290 ℃, and the exhaust gas is respectively introduced in the processes of coating B1000 ppm, washing, drying and coating.
Example 4: lithium complex m =1.06, x =0.85, y =0.08, z =0.07; the temperature M1=750 ℃, M2=830 ℃, M3=285 ℃, the coating B is 1000ppm, and waste gas is respectively introduced in the processes of water washing, drying and coating.
Example 5: lithium complex m =1.07, x =0.92, y =0.04, z =0.04; the temperature M1=700 ℃, M2=810 ℃, M3=280 ℃, and waste gas is respectively introduced in the processes of coating B1000 ppm, washing, drying and coating.
Example 6: lithium complex m =1.06, x =0.82, y =0.10, z =0.08; the temperature M1=770 ℃, the temperature M2=850 ℃, the temperature M3=550 ℃, the Al coating is 1000ppm, and waste gas is respectively introduced in the processes of washing, drying and coating.
Example 7: lithium complex m =1.06, x =0.82, y =0.10, z =0.08; the temperature M1=770 ℃, M2=850 ℃, M3=400 ℃, and exhaust gas is respectively introduced in the processes of coating Ti by 1000ppm, washing, drying and coating.
Comparative example 1 differs from example 1 only in that: no waste gas is introduced in the processes of washing, drying and coating.
Comparative example 2 differs from example 1 only in that: washing with water, drying and introducing waste gas, wherein no waste gas is introduced in the coating process.
Comparative example 3 differs from example 1 only in that: no waste gas is introduced during washing and drying, and waste gas is introduced during the coating process.
Test example 1
The performance of the positive electrode materials prepared in the examples and comparative examples was tested, and the results are shown in table 1.
The test method comprises the following steps: assembling the target materials into a button half cell: the materials prepared in the examples and the comparative examples, the conductive agent Super P and the adhesive PVDF are mixed according to the mass ratio of 90:5: 5. preparing nickel cobalt lithium manganate slurry by using a defoaming machine, adjusting the solid content of the slurry to 38% by using N-methylpyrrolidone (NMP), and then automatically using the adjusted slurryCoating on aluminum foil by a coating machine, drying at 120 ℃ in a vacuum drying box, rolling by a roller press, punching by a slicing machine, assembling a button 2025 battery in a glove box, wherein the electrolyte is 1.2mol/L LiPF 6 Wherein the solvent is EC: EMC =3 (volume ratio), the diaphragm is Celgard polypropylene membrane, and the metal lithium piece is adopted as the counter electrode. And (3) carrying out charge-discharge test on the button half cell in a voltage range of 3-4.3V on a blue tester. And (3) testing the first charging specific capacity, the first discharging specific capacity and the coulombic efficiency of 0.1C, and testing the capacity retention rate after 1C is cycled for 50 circles at 45 ℃.
The XRD patterns of the products prepared in the test examples and comparative examples are shown in fig. 2.
In the case where the material itself has no significant preferred orientation, (003) plane is a plane in which the transition metal is deposited, and (104) plane is a plane in which Li/TM is uniformly distributed. According to the X-ray diffraction theory, heavy atoms have stronger scattering ability. The intensity of the (003) diffraction peak should ideally be significantly stronger than the (104) diffraction peak. If the (003) plane is mixed with Li atoms, the (003) diffraction peak is lowered, resulting in a decrease in the intensity ratio of the two diffraction peaks. (006) The symbols of the layered structure are represented by (012) and (018)/(110), the two pairs of diffraction peaks being very close because the corresponding interplanar spacings are very close. In an ideal layered structure, two pairs of diffraction peaks are clearly separable in XRD; if the layered structure is destroyed, their corresponding interplanar spacings are closer together and the corresponding peak positions are closer together, resulting in an indistinguishable diffraction peak.
As can be seen from the figure, ternary materials with higher crystallinity are obtained in the examples 1 and the comparative examples 1 to 3
The peak splitting degrees of the materials (018) and (110) are obvious, which indicates that the materials maintain better layered structures. Table 1 lists the ratios of the (003) and (104) peak intensities for the different examples and comparative examples, and from the above data it can be seen that the degree of Li/Ni miscellany is lower for example 1 than for comparative example.
TABLE 1 results of performance test of products prepared in examples and comparative examples
| Item | I(003)/ I( 1 0 4 ) | 0.1C discharge capacity mA h/g | First effect/%) | 1C discharge capacity mA h/g | Cycle retention ratio/% (1C/1C, 45 ℃ C.) |
| Example 1 | 1.355 | 213.0 | 92.0 | 193 | 96.6 |
| Comparative example 1 | 1.266 | 211.2 | 90.4 | 191.3 | 94.6 |
| Comparative example 2 | 1.278 | 211.8 | 91.2 | 191.9 | 95.2 |
| Comparative example 3 | 1.289 | 212.3 | 91.3 | 192.3 | 95.5 |
| Example 2 | 1.428 | 194.2 | 90.2 | 173.3 | 98.2 |
| Example 3 | 1.386 | 202.8 | 90.5 | 182.5 | 97.7 |
| Example 4 | 1.326 | 215 | 92 | 194 | 96.2 |
| Example 5 | 1.278 | 221 | 92.3 | 200 | 95.6 |
| Example 6 | 1.357 | 208 | 91.6 | 187.5 | 97.8 |
| Example 7 | 1.353 | 210 | 91.8 | 199.6 | 96.3 |
In conclusion, the preparation method of the high-nickel low-cobalt cathode material provided by the invention can effectively and reasonably utilize waste gas generated in the preparation process of the high-nickel material, reduce the dissolution speed of LiOH on the surface in the washing process and delay the generation of NiO rock salt phase on the surface of the material. In addition, a similar lithium supplement agent is added in the coating process to react with the coating, which is beneficial to synthesizing the coating with better ionic conductivity in the secondary sintering process and improving the cycle performance of the material.
The present invention has been described in terms of the preferred embodiment, and it is not intended to be limited to the embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A preparation method of a high-nickel low-cobalt cathode material is characterized by comprising the following steps:
respectively sintering the prepared single crystal nickel-cobalt-manganese precursor and polycrystalline nickel-cobalt-manganese precursor with a lithium source in an oxygen atmosphere to obtain a nickel-cobalt-manganese single crystal material and a nickel-cobalt-manganese polycrystalline material, mixing the nickel-cobalt-manganese single crystal material and the nickel-cobalt-manganese polycrystalline material, then sequentially washing, carrying out solid-liquid separation and drying, mixing the dried material with a coating agent, and then carrying out secondary sintering;
wherein the particle size of the single crystal nickel cobalt manganese precursor is smaller than that of the polycrystalline nickel cobalt manganese precursor;
the preparation process of the water washing solution adopted in the water washing process comprises the following steps: mixing waste gas generated by primary sintering with water;
the atmosphere adopted in the drying process is selected from at least one of waste gas generated in the secondary sintering and waste gas generated in the primary sintering cooling section;
and introducing waste gas generated by primary sintering in the process of mixing the dried material and the coating agent.
2. The method according to claim 1, wherein the primary sintering process comprises:
mixing the single crystal nickel-cobalt-manganese precursor with a lithium source, and sintering for 10-15 h at 810-925 ℃ in an oxygen atmosphere to obtain the nickel-cobalt-manganese single crystal material;
mixing the polycrystalline nickel-cobalt-manganese precursor with a lithium source, and sintering for 8-12 h under the conditions of an oxygen atmosphere and 700-850 ℃ to obtain the nickel-cobalt-manganese polycrystalline material;
wherein the lithium source is selected from at least one of lithium hydroxide, lithium nitrate and lithium chloride;
the D50 of the single crystal nickel-cobalt-manganese precursor particles is 3-4 mu m, and the D50 of the polycrystalline nickel-cobalt-manganese precursor particles is 8-10 mu m.
3. The method of claim 2, wherein the single crystal nickel cobalt manganese precursor and the polycrystalline nickel cobalt manganese precursor have the chemical formula Ni x Co y Mn z (OH) 2 ，x+y+z＝1；x=0.65~0.95；y= (1-x)/(x+1)；
When the single crystal nickel cobalt manganese precursor and the polycrystalline nickel cobalt manganese precursor are sintered for one time, controlling the molar ratio of the precursor to lithium elements in the lithium source to be 1: m, m =1.04-1.07.
4. The preparation method according to claim 3, wherein the single crystal nickel cobalt manganese precursor and the polycrystalline nickel cobalt manganese precursor are prepared by a coprecipitation reaction, and the preparation process comprises the following steps:
mixing nickel salt, cobalt salt and manganese salt according to the molar ratio of nickel, cobalt and manganese of x, y and z, and carrying out coprecipitation under the condition of adding a precipitator and a chelating agent, wherein the coprecipitation process is controlled to be carried out under an inert atmosphere, the pH value of a system is controlled to be 10.5-11.5, the temperature is controlled to be 45-55 ℃, and when a precursor with a required size is obtained through deposition, washing and drying are carried out;
wherein the precipitant is 3-5 mol/L sodium hydroxide solution, and the chelating agent is 8-12 mol/L ammonia water solution.
5. The production method according to claim 1, wherein the process of blending the nickel-cobalt-manganese single-crystal material and the nickel-cobalt-manganese polycrystalline material comprises: crushing the nickel-cobalt-manganese single crystal material to a D50 of 3-5 μm, crushing the nickel-cobalt-manganese polycrystalline material to a D50 of 9-11 μm, and mixing the crushed nickel-cobalt-manganese single crystal material and the crushed nickel-cobalt-manganese polycrystalline material according to a mass ratio of 2.
6. The method of claim 1, wherein the aqueous cleaning solution is prepared by a process comprising: introducing waste gas generated by primary sintering into water, wherein the volume of the waste gas per liter of water is 3m 3 -5m 3 ；
During washing, the mixed material is placed in the washing solution and washed with water under the stirring condition; controlling the mass of the material which is correspondingly blended per liter of washing solution to be 0.5kg-2kg;
when washing with water, the stirring frequency is controlled to be 100Hz-200Hz, and the stirring time is controlled to be 10min-20min.
7. The preparation method according to claim 1, characterized in that solid-liquid separation is performed after water washing, the obtained solid material is dried under stirring, and waste gas is introduced at a rate of 40L/min to 60L/min during the drying process; controlling the stirring speed to be 50-200 rpm, and the drying time to be 4-8 h;
wherein, the solid-liquid separation is carried out by adopting a filter pressing mode.
8. The preparation method according to claim 1, characterized in that the dried material and the coating agent are mixed under the condition of waste gas generated in a primary sintering temperature rise region, and secondary sintering is carried out after mixing;
in the mixing process, the stirring speed is controlled to be 400rpm-800rpm, and the stirring time is controlled to be 20min-60min; controlling the sintering temperature of the secondary sintering to be 280-550 ℃ and the sintering time to be 4-8 h;
the coating agent is selected from at least one of boric acid, aluminum hydroxide and titanium oxide; the coating amount of the coating element is controlled to be 500ppm-1500ppm.
9. A high-nickel low-cobalt cathode material, which is prepared by the preparation method of any one of claims 1 to 8.
10. A lithium ion battery comprising the high nickel low cobalt positive electrode material of claim 9.
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